The invention pertains to a process for the biological and, optionally, the chemical treatment of sewage using aeration in aeration basins arranged concentrically within a basin, secondary settling basins and sludge collection as well as an installation for carrying out the process.
The design of biological sewage treatment installations in a number of stages with an activation stage and at least one secondary settling stage is known. These installations have the disadvantage that they manifest a large floor space requirement. In the case of flocculation installations, compact sewage treatment plants such as FR-A 1,081,214 are known, in which the intermingling with the flocculator takes place in a central basin and the secondary settling in a surrounding ring basin. In addition, a two-stage treatment plant of tower design is known from CH-A 462,273, in which a treatment of the sewage is achieved though precipitation.